Homogenous catalyst solutions prepared from transition metals and phosphorus ligands are used widely in the chemical industry. The advantages of homogenous catalysts over heterogeneous catalysts usually include higher reactivity and higher selectivity. However, homogenous catalysts often are subject to degradation and concomitant loss of activity over time. The problem of catalyst degradation is aggravated if the degradation process leads to the formation of unwanted side products that are found as contaminants in the product Therefore, it is highly desirable to develop technologies that extend the effective catalyst lifetime, enhance selectivity and reduce contaminants in the product.
The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. The most extensive use of the reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amounts of the normal to iso aldehyde products typically is referred to as the normal to iso (N:I) or the normal to branched (N:B) ratio. In the case of propylene, the normal- and iso-butyraldehydes obtained from propylene are in turn converted into many commercially-valuable chemical products such as, for example, n-butanol, 2-ethyl-hexanol, n-butyric acid, iso-butanol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, the mono-isobutyrate and di-isobutyrate esters of 2,2,4-trimethyl-1,3-propanediol. The hydroformylation of higher α-olefins such as 1-octene, 1-hexene, and 1-decene yield aldehyde products which are useful feedstocks for the preparation of detergent alcohols and plasticizer alcohols. The hydroformylation of substituted olefins such as allyl alcohol is useful for the production of other commercially valuable products such as 1,4-butanediol.
Catalysts used in the hydroformylation reaction typically contain rhodium complexes comprising at least one phosphorus ligand. U.S. Pat. No. 3,239,566, issued Mar. 8, 1966, to Slaugh and Mullineaux, discloses a low pressure hydroformylation process using trialkylphosphines in combination with rhodium catalysts for the preparation of aldehydes. Trialkylphosphines have seen much use in industrial hydroformylation processes but they typically produce a limited range of products and, furthermore, frequently are very oxygen sensitive. U.S. Pat. No. 3,527,809, issued Sep. 8, 1970 to Pruett and Smith, discloses a low pressure hydroformylation process which utilizes triarylphosphine or triarylphosphite ligands in combination with rhodium catalysts. The ligands disclosed by Pruett and Smith, although used in many commercial applications, have limitations due to oxidative and hydrolytic stability problems. Since these early disclosures, numerous improvements have been made to increase the catalyst stability, catalyst activity and the product ratio with a heavy emphasis on yielding linear aldehyde product. A wide variety. of monodentate phosphite and phosphine ligands, bidentate ligands such as bisphosphites and bisphosphines as well as tridentate and polydentate ligands have been prepared and disclosed in the literature. U.S. Pat. No. 5,840,647 discloses the use of diorgano-fluorophosphites, also known as fluorophosphites, as the phosphorus ligand component of hydroformylation catalysts.
It also is known that the hydroformylation catalysts suffer from the drawback that the phosphorus ligands can be decomposed by a variety of mechanisms including oxidation, acid catalyzed hydrolysis, and, in the case of certain tri-organo phosphite ligands, the rhodium-catalyzed decomposition of the phosphite as disclosed in U.S. Pat. Nos. 5,756,855 and 5,929,289. The ligand decomposition reactions are detrimental to the overall economics of the process as they result in the loss of the valuable ligand and also can result in the formation of ligand degradation products which may act as catalyst poisons. We have found that diorgano fluorophosphite compounds described in U.S. Pat. No. 5,840,647 undergo low level degradation to generate hydrogen fluoride with concomitant loss of ligand. The hydrogen fluoride contaminates the product aldehydes which is highly undesirable as it can lead to corrosion and the formation of by-products.